Computer virus
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A computer virus is a piece of unauthorized software added to a computer which automatically spreads itself to other computers. Some viruses do malicious things, such as erasing files or copying sensitive information (like passwords and credit card numbers).
Process of transmission
There are three main ways a virus is transmitted.
- Automatic replication. When you run an infected program, the virus also runs, searching your computer for other programs to infect.
- By email. When email software is configured to run programs attached to messages, the virus sends itself to recipients in your address book.
- Misleading advertising. A "Trojan Horse" is a program which seems useful, but contains a virus. The main program may or not perform as advertised, but the distributor knows it is infected.
A virus which infects networks is called a "worm".
A Trojan Horse virus typically does not replicate itself but is spread when you copy the program.
Discussion of the virus problem is sometimes hampered by the terminology used by purists, who distinguish between such varieties as "worm", "Trojan Horse", etc. But the generic term for unwanted software that infects your computer is "virus".